This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. For mammals, acquired immunity is achieved by transferring IgG from mother to young through a receptor called FcRn, which binds IgG at acidic pH in the neonatal small intestine and releases it at basic pH into blood. FcRY is an avian functional equivalent of FcRn, but belongs to a different structural family which includes phospholipase A2 receptor. FcRY binds IgY, the avian counterpart of IgG, and transfers it across yolk sac membranes. It has been shown that the ectodomain of FcRY has a large conformational change between acidic and basic pH which corresponds to the binding and the releasing of IgY. However, the structural details of this conformational change are unclear. Here we propose to use SAXS to investigate the conformational change of FcRY and its binding with IgY. This could improve our current understanding of the mechanisms of acquired immunity and also the strategies against avian- associated human diseases.